US 7126318 B2 Abstract A method of generating a slope compensation signal for use in a current mode switching regulator. The method includes the steps of summing a clock signal and a reference signal so as to generate a linear ramp signal; generating a non-linear signal from the linear ramp signal; multiplying a correction signal with an input voltage signal so as to generate a signal which varies based on a measured value of a current flowing within the current mode switching regulator; summing a first voltage signal corresponding to the non-linear correction signal and a second voltage signal indicating the difference between an actual voltage level of the current mode switching regulator and the desired voltage level of the current mode switching regulator so as to generate a first output signal which represents the second voltage signal minus the first voltage signal; and comparing the first output signal and the measured value of a current flowing within the current mode switching regulator, and generating a second output signal utilized to control current flow within the current mode switching regulator based on the result of the comparison.
Claims(19) 1. A slope compensation circuit for use in a current mode switching regulator, said slope compensation circuit comprising:
a first summer circuit for receiving a clock signal and a reference signal as input signals, and for generating a linear signal as an output signal;
a multiplier and integrator circuit for multiplying said linear signal with an input voltage signal, and integrating the result for generating a non-linear signal which varies based on a measured value of a current flowing within said current mode switching regulator;
a second summer circuit for receiving a first voltage signal corresponding to said non-linear signal and a second voltage signal indicating the difference between an actual voltage level of said current mode switching regulator and the desired voltage level of said current mode switching regulator, and for generating a first output signal which represents the second voltage signal minus the first voltage signal; and
a comparator for receiving the first output signal from said second summer as a first input, and said measured value of a current flowing within said current mode switching regulator as a second input, and for generating a second output signal utilized to control current flow within said current mode switching regulator.
2. The slope compensation circuit of
3. The slope compensation circuit of
4. The slope compensation circuit of
5. The slope compensation circuit of
6. The slope compensation circuit of
7. The slope compensation circuit of
8. The slope compensation circuit of
9. A current mode switching regulator for regulating an output voltage, said current mode switching regulator comprising:
a switch;
a controller coupled to said switch, said controller governing the operational state of said switch so as to control current flow to a load; and
a slope compensation circuit; said slope compensation circuit including:
a first summer circuit for receiving a clock signal and a reference signal as input signals, and for generating a linear signal as an output signal;
a multiplier and integrator circuit for multiplying said linear signal with an input voltage signal, and integrating the result for generating a non-linear signal which varies based on a measured value of a current flowing within said switch;
a second summer circuit for receiving a first voltage signal corresponding to said non-linear signal and a second voltage signal indicating the difference between an actual voltage level of said current mode switching regulator and the desired voltage level of said current mode switching regulator, and for generating a first output signal which represents the second voltage signal minus the first voltage signal; and
a comparator for receiving the first output signal from said second summer as a first input, and said measured value of a current flowing within said switch regulator as a second input, and for generating a second output signal utilized to control current flow through said switch.
10. The current mode switching regulator of
11. The current mode switching regulator of
12. The current mode switching regulator of
13. The current mode switching regulator of
14. The current mode switching regulator of
15. A method of generating a slope compensation signal for use in a current mode switching regulator, said method comprising the steps of:
summing a clock signal and a reference signal so as to generate a linear ramp signal;
multiplying said linear ramp signal with an input voltage signal so as to generate a scaled signal which varies based on a measured value of a current flowing within said current mode switching regulator;
integrating the linear scaled signal with respect to time to generate a non-linear ramp signal;
summing a first voltage signal corresponding to said non-linear signal and a second voltage signal indicating the difference between an actual voltage level of said current mode switching regulator and the desired voltage level of said current mode switching regulator so as to generate a first output signal which represents the second voltage signal minus the first voltage signal; and
comparing the first output signal and said measured value of a current flowing within said current mode switching regulator, and generating a second output signal utilized to control current flow within said current mode switching regulator based on the result of said comparison.
16. The method of
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Description This disclosure generally relates to improved switching regulator circuits, and more specifically, to methods and circuits to effectively implement higher order slope compensation in fixed frequency current mode switching regulator circuits. Current-mode switching regulators operate to provide a substantially constant output voltage to a load from a voltage source that may be poorly-specified or fluctuating. As is well known, in a current mode switching regulator, the flow of current to the load is provided in the form of discrete current pulses, and governed by a controller. The controller functions to measure the current flow within the regulator, and operate a switch contained within the regulator to control the current supply based on this measured current. By controlling the duty cycle of this switch, i.e., the percentage of time that the switch is ON relative to the total period of the switching cycle, the amount of current supplied by switching regulator can be regulated so as to provide the desired output level. In current-mode switching voltage regulators, which utilize current programmed control, there is an inherent instability when the duty cycle exceeds 50% with fixed frequency and continuous inductor current mode, and 67% with fixed frequency and discontinuous inductor current mode (i.e., when the switch is ON for more than 50% or 67% of a given switching period). In order to maintain stability of such current-mode switching regulators, the current-derived signal used to control the regulator is modified by, for example, applying a slope compensation signal. The timing circuit As noted above, it is well known in the prior art that slope compensation can be applied to the switching regulator controllers to avoid sub-harmonic oscillation instability of the duty cycle with respect to the switching frequency when the nominal duty cycle exceeds 50%. As set forth by Erickson, for buck converters the boundary of stability with slope compensation is stated as:
The preceding equations defining the waveforms are illustrated in As noted, the present design practice is usually to make the slope of the compensation signal constant at the maximum value required for a duty cycle equal to 100% (i.e., D=1) so that the waveform is an easy to generate linear ramp as illustrated in In other words, by utilizing a linear slope compensation signal and providing enough slope compensation to handle the worst case scenario, which is 100% duty cycle, the dynamic range of the controller is unnecessarily reduced when the regulator is operating at a duty cycle of less than 100%. As is known, the amount of slope compensation necessary to provide stability increases as the duty cycle increases. In view of the foregoing, it is desirable to provide only the amount of slope compensation actually required to prevent instability so as to not degrade the dynamic range of the controller. In view of the foregoing, it is a primary objective of the invention to solve the foregoing problems and provide a method and apparatus that allows for the addition of only the amount of slope compensation necessary to maintain stability of the regulator. In other words, the amount of slope compensation provided by the present invention varies in accordance with variations in the duty cycle during operation of the regulator. Moreover, the present invention provides for a varying slope compensation signal utilizing a simple, cost effective circuit, which results in practical solution to the aforementioned problems. According to one embodiment, the present invention relates to a method of generating a slope compensation signal for use in a current mode switching regulator. The method includes the steps of summing a clock signal and a reference signal so as to generate a signal that is zero in the interval from 0 to Ts/2 and a linear ramp signal from Ts/2 to Ts; multiplying the linear ramp signal with an input voltage signal so as to make the magnitude of the linear ramp signal vary proportional to the measured value of a current flowing within the current mode switching regulator; taking the time integral of this signal to create a non-linear signal; summing a first voltage signal corresponding to the non-linear signal and a second voltage signal indicating the difference between an actual voltage level of the output of the current mode switching regulator and the desired output voltage level of the current mode switching regulator so as to generate a first output signal which represents the second voltage signal minus the first voltage signal; and comparing the first output signal and the measured value of a current flowing within the current mode switching regulator, and generating a second output signal utilized to control current flow within the current mode switching regulator based on the result of the comparison. In another embodiment, the present invention relates to a slope compensation circuit for use in a current mode switching regulator. The slope compensation circuit includes a first summer circuit for receiving a clock signal and a reference signal as input signals, and for generating a linear signal as an output signal; a multiplier circuit for multiplying said linear signal with an input voltage signal, generating a signal which varies proportional to the measured value of a current flowing within said current mode switching regulator; an integrator circuit for taking the time integral of the multiplier output; a second summer circuit for receiving a first non-linear voltage signal corresponding to said integrator output signal and a second voltage signal indicating the difference between an actual voltage level of said current mode switching regulator and the desired voltage level of said current mode switching regulator, and for generating an output signal which represents the second voltage signal minus the first voltage signal; and a comparator for receiving the output signal from said second summer as a first input, and said measured value of a current flowing within said current mode switching regulator as a second input, and for generating an output signal utilized to control current flow within said current mode switching regulator. The slope compensation circuit of the present invention provides numerous advantages over the prior art. One advantage is that the amount of slope compensation provided by the present invention varies in accordance with variations in the duty cycle during operation of the regulator such that only the amount of slope compensation necessary to prevent instability is provided. As such, there is no degradation in the dynamic range of the controller, which results when slope compensation in excess of what is required is provided to the regulator. Another advantage of the present invention is that the variable slope compensation signal is provided utilizing a simple, cost effective circuit, thereby providing a practical solution to the aforementioned problems of the prior art. This is accomplished in part due to the fact that the controller of the present invention only requires the high-side switch current and output voltage as measured variables. Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following description, or may be learned by practice of the invention. While the novel features of the invention are set forth below, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several aspects and embodiments of the present invention and, together with the general description given above and detailed description given below, serve to explain the principles of the invention. Such description makes reference to the annexed drawings. The drawings are only for the purpose of illustrating preferred embodiments of the invention and are not to be treated as limiting the invention. In the drawings: Throughout the above-mentioned drawings, identical reference numerals are used to designate the same or similar component parts in most instances. The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein: rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art, like numbers refer to like elements throughout. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present disclosure. Referring to
Circuit It is noted that signal V As noted above, in order to maintain stability, the slope compensation signal, Ve(t), as set forth in equations (6) and (7) equals: Thus, the time dependence required in equations (6) and (7) can be obtained from the clock waveform: It is noted that in the signal processing occurring in the present invention, there are parameters that are constant and fixed, and parameters that vary as functions of time and therefore have inherent time dependence. In the exemplary implementation disclosed herein, the circuit components R, L, C, etc. are all fixed values and only the currents and voltages vary as a function of time, and therefore have time dependence. In this regard it is noted that equation (12) defines the output of the first summer The output of the first summer The third transconductance amplifier
It is noted again that the slope compensation circuit
The other signal input into the multiplier circuit It is noted that all of the sensed currents and voltages utilized in the slope compensation circuit of the present invention are scaled versions relative to the actual current and voltage values. This scaling is utilized in order to increase the overall implementation efficiency of the slope compensation circuit and to minimize power dissipation, so it is a practical necessity. Thus, as It is noted that one of the important aspects of the present invention is the use of the time domain integrator As mentioned above, the slope compensation circuit of the present invention provides numerous advantages over the prior art. Most importantly, the amount of slope compensation provided by the circuit of the present invention varies in accordance with variations in the duty cycle during operation of the regulator such that only the amount of slope compensation necessary to prevent instability is provided. In other words, the slope of the compensation signal is a non-linear continuous function of the duty cycle of the regulator. As such, there is no additional degradation in the dynamic range of the controller, which results when slope compensation in excess of what is required is provided to the regulator. Another advantage of the present invention is that the variable slope compensation signal is provided utilizing a simple, cost effective circuit, thereby providing a practical solution to the aforementioned problems of the prior art. Furthermore, the only measured variables are those already used by a conventional current mode switching regulator. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all generic and specific features herein described and all statements of the scope of the various inventive concepts which, as a matter of language, might be said to fall therebetween. Patent Citations
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